A display panel provided with a solar cell (solar battery) requires an optical transparency so as to transmit a light that has been received and to enable the solar cell disposed on the lower surface side of the display panel to generate an electric power. Therefore, a translucent material such as plastic, ceramic, and glass is used for the display panel. In particular, plastic is used extensively at least since plastic is moderate in price and the shape forming and processing of plastic can be easily carried out.
FIG. 48 is a plan view showing a general solar cell.
As shown in FIG. 48, a general solar cell is formed in each of four faces (A1, A2, A3, and A4) that have been equally segmented and is disposed on the lower surface side of a display panel. A transmission light that has been transmitted to the display panel is uniformly irradiated to each of the four faces (A1, A2, A3, and A4), thereby resulting in the highest electric power generation efficiency. Consequently, it is necessary to design the display panel that is disposed on the upper surface side of the solar cell in such a manner that a uniform amount of lights are transmitted to each of sections corresponding to the four faces (A1, A2, A3, and A4) of the solar cell, that is, each of four faces that have been equally segmented by the 12-6 o'clock line and the 9-3 o'clock line.
However, the solar cell that is disposed on the lower surface side of a display panel has a generic dark purplish color, and a cross line for the segmentation into four equal divisions is extremely conspicuous due to a difference in materials. Consequently, the solar cell spoils the beauty thereof. To soften the dark purplish color or make the dark purplish color invisible, many ideas have been carried out for the display panel.
A conventional example of a display panel provided with a solar cell will be described below with reference to the drawings.
FIG. 49 is a partially enlarged cross-sectional view showing the structure of a dial plate for a watch provided with a solar cell as a display panel in a conventional art. FIG. 50 is a schematic perspective view showing a reflection polarizing substance in which a plurality of layers are laminated as a component part of a display panel in a conventional art.
As shown in FIG. 49, a dial plate 100 for a solar watch in a conventional art is composed of a substrate 101, a polarizing substance 103 formed on the side of a substrate 101 surface facing a solar battery 109, and a diffusing layer 102 disposed between the substrate 101 and the polarizing substance 103. In addition, a time character, a decorated character, and a mark or the like are arranged on the substrate 101.
The substrate 101 is made of a light transmitting material such as glass and plastic such as an acrylic resin and a polycarbonate resin, and is in a planar shape having a thickness in the range of 300 to 600 μm. To prevent the original color of the solar battery 109 from being seen through, a colored layer is formed on the substrate 101 by a method such as a coating method, a printing method, a wet plating method, and a dry plating method in some cases. It is disclosed that the colored layer is preferably white.
The diffusing layer 102 is made of a material containing a diffusing agent having a function for diffusing a light that has been irradiated. As a diffusing agent configuring the diffusing layer 102, a material such as silica, glass, and a resin having a shape in a granular state (powdered state), a scale-like state, or an acicular state is used, and a diffusing agent made of a material having a self-bonding property or an adhesion property is disclosed for instance.
The reflection polarizing substance 103 has a function for polarizing a light that has been irradiated. More specifically, the reflection polarizing substance 103 has a function for transmitting a first light vibrating in a predetermined direction and a function for reflecting a second light having a vibration direction perpendicular to the direction of vibration of the first light.
As shown in FIG. 50, the reflection polarizing substance 103 has a laminated body in which a plurality of layers is laminated. More specifically, the reflection polarizing substance 103 has a structure in which a plurality of polarizing film layers (A layers) 131 and polarizing film layers (B layers) 132 are laminated alternately.
As the A layer 131 of the reflection polarizing substance 103, a stretched film made of polyethylene naphthalate is used for instance. As the B layer 132, a material made of copolyester composed of naphthalenedicarboxylic acid and terephthalic acid is disclosed for instance.
As described above, a dial plate 100 for a solar watch as a display panel in a conventional art is composed of a light transmitting substrate 101, a diffusing layer 102, and a reflection polarizing substance 103, thereby having a sufficiently high optical transparency. In addition, it is also disclosed that the original color of the solar battery 109 can be prevented from being seen through, and a decorative effect can be displayed.
(See Patent Document 1 for Instance.)
Patent document 1: International Publication WO2006/006390 (pages 5 to 11, FIGS. 1 and 2)
However, for a display panel in a conventional art, a metal sense like a metal display panel and a brilliant color with whiteness and brightness cannot be obtained. Consequently, it is difficult to obtain a display panel having the appearance quality with sophistication. In particular, for a display panel in a conventional art, a metal sense that is peculiar to a metal cannot be obtained and a design variation is poor disadvantageously.
The present invention was made in consideration of such conditions, and an object of the present invention is to provide a display panel having an improved decorative effect in which lights of an amount sufficient for an electric power generation in a solar cell can be obtained, and a cross line and a dark purplish color of a solar cell can be prevented from being seen.
Another object of the present invention is to provide a display panel having the appearance quality with sophistication in which a metal sense like a metal display panel and a brilliant color with whiteness and brightness can be obtained and to achieve an improved design variation and a thin-shaped profile of a display panel.
Another object of the present invention is to provide an apparatus in which the above display panel is used as a display panel for a clock, a measuring instrument panel of an electronic desk calculator, an automobile, and an airplane, and a display panel of an apparatus like a mobile apparatus such as a cellular phone.